The present invention relates to a color feature extracting apparatus, color feature extracting method and program storage medium thereof for extracting the color features of an image in an image database apparatus or the like.
Conventionally, when retrieving similar images in an image database, a similarity is decided by a color and an occupation ratio of the color to each image by classifying the color features of the images according to each specified color and giving the classified color as a key to the images or giving the color features directly to the image information. As a color feature extracting apparatus for use in retrieving such similar images, there is proposed one which extracts the color features of a digital image, each pixel of which is expressed by RGB (Red, Green and Blue) values, directly in the RGB color space.
However, the above color feature extracting apparatus has the drawback that color feature extraction cannot be executed through color classification or color region distinction conforming to the human sense because the human sense is hard to distinguish a color difference in the green region when the distinction is made by directly evaluating the RGB values.
In view of the above, it can be considered to use the color space of L*a*b* color space (JIS Z8729-(1980)) for equalizing the distance of color difference. However, the L*a*b* color space has difficulties in being subjected to a transformation since greater importance is attached to the accuracy of color difference, and the way of color-expression is disadvantageously less familiar to the ordinary people.